ProcessEngine processEngine = ProcessEngines.getDefaultProcessEngine();
RuntimeService runtimeService = processEngine.getRuntimeService();
RepositoryService repositoryService = processEngine.getRepositoryService();
TaskService taskService = processEngine.getTaskService();
ManagementService managementService = processEngine.getManagementService();
IdentityService identityService = processEngine.getIdentityService();
HistoryService historyService = processEngine.getHistoryService();
FormService formService = processEngine.getFormService();
DynamicBpmnService dynamicBpmnService = processEngine.getDynamicBpmnService();1. RepositoryService
The RepositoryService is probably the first service needed when working with the Activiti engine.
This service offers operations for managing and manipulating deployments and process definitions
2. RuntimeService
It deals with starting new process instances of process definitions
3.IdentityService
The IdentityService is pretty simple. It allows the management (creation, update, deletion, querying, …) of groups and users
4.FormService
The FormService is an optional service. Meaning that Activiti can perfectly be used without it, without sacrificing any functionality
A start form is a form that is shown to the user before the process instance is started, while a task form is the form that is displayed when a user wants to complete a form